A CMake lib include & use other third party lib as git submodule, when use main lib in other project, error report that third party lib are missing

Are you tired of dealing with the frustration of using third-party libraries as Git submodules in your CMake project, only to encounter errors when trying to use your main library in another project? You’re not alone! In this article, we’ll dive into the world of CMake and Git submodules, exploring the common pitfalls and providing a step-by-step guide on how to overcome them.

Understanding the Problem

The issue arises when you create a CMake library (let’s call it `MyLib`) that depends on a third-party library (e.g., `ThirdPartyLib`) as a Git submodule. When you try to use `MyLib` in another project, the build process fails, complaining that the third-party library is missing.

Why Does This Happen?

The reason behind this problem lies in how CMake handles dependencies and Git submodules. When you add a Git submodule to your project, CMake doesn’t automatically include the submodule’s dependencies in the build process. This leads to a mismatch between the dependencies required by `MyLib` and the dependencies available in the consuming project.

Solution: Configuring CMake and Git Submodules

To overcome this issue, we need to configure CMake to properly include the third-party library as a dependency and ensure that it’s propagated to the consuming project. Let’s break it down into smaller, manageable steps:

Step 1: Add the Third-Party Library as a Git Submodule

$ git submodule add https://github.com/third-party/ThirdPartyLib.git ThirdPartyLib
$ git submodule init
$ git submodule update --init --recursive

Make sure to update your `.gitmodules` file to include the submodule:

[submodule "ThirdPartyLib"]
  path = ThirdPartyLib
  url = https://github.com/third-party/ThirdPartyLib.git

Step 2: Configure CMake to Use the Git Submodule

In your `CMakeLists.txt` file, add the following code:

cmake_minimum_required(VERSION 3.10)
project(MyLib)

# Add the ThirdPartyLib submodule
add_subdirectory(ThirdPartyLib)

Step 3: Include the Third-Party Library in Your Main Library

In the same `CMakeLists.txt` file, include the third-party library:

# Include the ThirdPartyLib headers
include_directories(${ThirdPartyLib_SOURCE_DIR}/include)

# Link against the ThirdPartyLib library
link_directories(${ThirdPartyLib_SOURCE_DIR}/lib)

Consuming the Main Library in Another Project

Now that we’ve configured `MyLib` to properly include the third-party library, let’s create a new project that consumes `MyLib`:

Step 1: Add the Main Library as a Git Submodule

$ git submodule add https://github.com/my-project/MyLib.git MyLib
$ git submodule init
$ git submodule update --init --recursive

Update your `.gitmodules` file to include the submodule:

[submodule "MyLib"]
  path = MyLib
  url = https://github.com/my-project/MyLib.git

Step 2: Configure CMake to Use the Main Library

In your consuming project’s `CMakeLists.txt` file, add the following code:

cmake_minimum_required(VERSION 3.10)
project(ConsumerProject)

# Add the MyLib submodule
add_subdirectory(MyLib)

Step 3: Link Against the Main Library

In the same `CMakeLists.txt` file, link against `MyLib`:

# Link against MyLib
link_directories(${MyLib_SOURCE_DIR}/lib)
target_link_libraries(ConsumerProject MyLib)

Troubleshooting Common Issues

If you encounter issues during the build process, here are some common pitfalls to watch out for:

• Missing Dependencies: Ensure that all dependencies required by `MyLib` are properly included in the consuming project.
• Inconsistent Versions: Verify that the version of `ThirdPartyLib` used in `MyLib` matches the version used in the consuming project.
• Incorrect Paths: Double-check that the paths to the `ThirdPartyLib` and `MyLib` libraries are correct in both the producing and consuming projects.

Conclusion

By following these steps and understanding the intricacies of CMake and Git submodules, you can successfully use third-party libraries as Git submodules in your CMake project and easily consume your main library in other projects. Remember to carefully configure your dependencies, include paths, and link libraries to avoid common pitfalls.

Keyword	Description
CMake	A cross-platform build system generator
Git Submodule	A Git repository within another Git repository
Third-Party Library	A library developed and maintained by a third-party organization
Main Library	A library developed and maintained by your organization

Additional Resources

For a deeper understanding of CMake and Git submodules, we recommend the following resources:

• CMake Documentation
• Git Submodule Documentation
• Example Project: CMake with Git Submodule

By mastering the art of using third-party libraries as Git submodules in your CMake project, you’ll be able to create more robust, maintainable, and scalable software systems.

Frequently Asked Question

Are you tired of dealing with CMake library includes and third-party libraries as Git submodules? Don’t worry, we’ve got you covered! Here are some frequently asked questions and answers to help you navigate these issues.